Power saving method in wireless communication system

ABSTRACT

A method and apparatus of accessing a channel in a wireless local area network is provided. A destination station receives a request to send (RTS) frame to allocate a network allocation vector from a source station over a first bandwidth and transmits a clear to send (CTS) frame over a second bandwidth to the source station in response to the RTS frame. The second bandwidth is dynamically determined when a first parameter has a predetermined value.

CROSS REFERENCES

The present application is a continuation of U.S. patent applicationSer. No. 13/458,940, filed on Apr. 27, 2012, which is a continuation ofpatent application number PCT/KR2010/007494, which claims priority ofKorean patent application number 10-2009-0103008, filed on Oct. 28,2009, which are incorporated by reference in their entirety.

TECHNICAL FIELD

Exemplary embodiments of the present invention relate to a method forincreasing resource utilization of a high-rate wireless communicationsystem and reducing power consumption, and a controlling apparatustherefor.

BACKGROUND ART

As a wireless communication system has been advanced and a demand forportably available high-capacity multimedia contents has been increased,many efforts have been made to increase a data transfer rate of awireless communication system. Representative examples are a Wibro whichcan use the Internet during a high-speed movement, and a wireless LANwhich can watch high-quality images during a low-speed movement in realtime. A wireless LAN will be exemplarily described. The IEEE 802.11a/gstandard supports a 54 Mbps physical layer data rate through a singleantenna at a 20-MHz bandwidth in a 2.4-GHz or 5-GHz band. The IEEE802.11n standard supports up to four antennas and a 40-MHz bandwidth andthus supports a 600-Mbps physical layer data rate.

As the next generation wireless LAN for ensuring a higher data rate, anext version of the IEEE 802.11n standard is under discussion. Ingeneral, the IEEE 802.11n standard is called a high throughput (HT)mode, and the IEEE 802.11a/b/g mode is called a legacy mode. On theother hand, the standard which has been newly discussed in the IEEE802.11ac/ad is called a very high throughput (VHT) mode.

To process high-rate data with high reliability, a recent wirelesscommunication system has become more complicated, as compared to aconventional art. As a data rate improvement technique, a channelbonding technique which bonds multi-channels and transmits data over thebonded channels is applied. In addition, a higher order modulationscheme and channel coding scheme have been introduced. In addition to atechnique which increases a data rate with the use of multi-antennas, atechnique which simultaneously transmits data to multi-users has beenresearched and developed. Due to such a complicatedtransmission/reception technique, the size of a wireless communicationsystem increases and the circuitry thereof becomes complicated.Furthermore, since data is transmitted using a wider bandwidth than aconventional art in order for a high-rate data transmission, therequired operating frequencies of a digital-to-analog converter (DAC),an analog-to-digital converter (DAC), and a modem processor have beenincreased. On such a technical background, a power save design for adynamic channel bandwidth utilization technique and a high-data-ratewireless communication system has become an important issue as areceiver optimization technique for efficiently using finite frequencyresources and reducing noise.

In addition, a wireless LAN operates at a limited frequency band. A160-MHz bandwidth (bonding of eight 20-MHz bands) is relatively verywide band. Accordingly, interference and coexistence problems may occurbetween stations which support various standards. Therefore, there is aneed for a technique which optimizes a receiving end by informingstations of preceding information through a control frame prior to adata frame in order to detect a multi transfer mode frame with highreliability.

DISCLOSURE Technical Problem

An embodiment of the present invention is directed to a transmissionmethod which improves a technique for a power save design at both aphysical layer and a MAC layer and improving the efficiency of a powersave technique, and a controlling apparatus therefor.

Another embodiment of the present invention is directed to a method forimproving power consumption efficiency by controlling the sampling ratesof an ADC, a DAC, and a modem processor according to a channel bandwidthused in a next generation wireless LAN, and a controlling apparatustherefor.

Another embodiment of the present invention is directed to a method andapparatus for transmitting a control frame containing precedinginformation in order to reduce noise and optimize the architecture of areceiving end according to a kind of a frame to be received.

Technical Solution

In accordance with an embodiment of the present invention, a frametransmitting method in a wireless communication system having two ormore different bandwidth transmission modes includes: transmittingchannel state information or data frame mode information added to arequest frame, upon transmission of a request frame; and generating andtransmitting the data frame, based on the channel state information orthe receivable data frame mode information contained in a responseframe, upon reception of the response frame with respect to the requestframe including the channel state information or the receivable dataframe mode information from a reception node.

In accordance with another embodiment of the present invention, a powersaving method in a wireless communication system having two or moredifferent bandwidth transmission modes includes: receiving a controlframe by setting the control frame to be received in a mode having thelowest sampling rate among the bandwidth modes, upon reception of thecontrol frame; and transmitting/receiving a data packet by setting thedata packet to be transmitted/received in a mode having the highestsampling rate in order for transmission/reception of the data packetafter the control frame is received.

In accordance with another embodiment of the present invention, a powersaving method in a wireless communication system whichtransmits/receives data through a carrier sensing includes: supplyingpower to only a timer for releasing the doze mode and interrupting thesupply of power to an entire physical layer and an entire MAC layer in adoze mode in which the sensing carrier is unnecessary; supplying powerto only a physical layer and a MAC layer necessary for the carriersensing when the carrier sensing is required; and supplying power toonly a path necessary for data transmission/reception when the datatransmission/reception is required after the carrier sensing.

In accordance with another embodiment of the present invention, a powersaving method in a wireless communication system which has two or moredifferent transmission modes and transmits/receives data through acarrier sensing includes: supplying power to only a timer for releasingthe doze mode and interrupting the supply of power to an entire physicallayer and an entire MAC layer in a doze mode in which the sensingcarrier is unnecessary; performing the carrier sensing in a mode havingthe lowest sampling rate among the different bandwidth modes, when thecarrier sensing is required; and transmitting/receiving the data packetby setting the data packet to be transmitted/received in a mode havingthe highest data rate in order for transmission/reception of the datapacket after the carrier sensing.

Advantageous Effects

In accordance with embodiments of the present invention, the powerconsumption efficiency can be improved by selectively changing thesampling rate of the station and the power supply block according to theframe format and the operation mode of the high-rate wirelesscommunication system. In addition, the disadvantages of the power savemode using the control of the conventional MAC layer can becomplemented. A wider bandwidth can be used and the power consumptionefficiency of the next generation wireless LAN to be more complicatedcan be improved.

DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are block diagrams of a wireless communication stationhaving three reception paths.

FIG. 2 is a flowchart in a power save mode change in accordance with anembodiment of the present invention.

FIG. 3 is a timing diagram for helping the understanding of theoperation principle of four reception modes in accordance with anembodiment of the present invention.

FIG. 4 is a finite state machine of a cross layer power save mode 2.

FIG. 5 is a timing diagram for helping the understanding of a powercontrol step in accordance with an embodiment of the present invention.

FIG. 6 is a flowchart of a change procedure in a multi-channel powersave mode in accordance with an embodiment of the present invention.

FIGS. 7 and 8 are timing diagrams for noise reduction and a multi-modeframe coexistence in accordance with an embodiment of the presentinvention.

FIG. 9 is a diagram for explaining the operation of the presentinvention in an overlapped basic service set (OBSS) situation.

MODE FOR INVENTION

Exemplary embodiments of the present invention will be described belowin more detail with reference to the accompanying drawings. The presentinvention may, however, be embodied in different forms and should not beconstrued as limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. Throughout the disclosure, like referencenumerals refer to like parts throughout the various figures andembodiments of the present invention.

The present invention relates to a method for improving powerconsumption efficiency for a high-rate wireless communication system,and a controlling technique therefor. The present invention is roughlydivided into three parts. The respective parts can operate independentlyor interwork with one another. The first part is three cross layer powersave mode, the second part is a transmission part for improvingefficiency of a power save mode, and the third part is a power savetechnique using a multi-channel power save mode (MC PS mode) and aspatial multiplexing power save mode (SM PS mode).

First, power consumption (P) of a general CMOS circuit will be describedbelow. The power consumption (P) of the CMOS circuit is modeled asexpressed in as shown:

$\begin{matrix}\begin{matrix}{P = {P_{Dynamic} + P_{Static}}} \\{= {{C \cdot V_{Sig} \cdot V_{DD} \cdot f_{0} \cdot n_{t}} + {V_{DD} \cdot I_{Static} \cdot ^{\frac{V_{DD}}{{pV}_{T}}}}}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

where P_(Dynamic) denotes a dynamic power consumption, P_(Static)denotes a static power consumption, C denotes a switched totalcapacitance, V_(Sig) denotes a voltage swing, V_(DD) denotes a supplypower, F₀ denotes an operating frequency and N_(t) denotes a number oftransition of one flip-flop per clock.

According to Equation 1 above, P_(Dynamic) is proportional to theswitched total capacitance, the voltage swing, the supply power, theoperating frequency, and the number of transition of one flip-flop perclock. In addition, P_(Static) is determined by the residual current ofthe ground or the supply power, a thermal noise, and a current generatedby a process. That is, P_(Static) is an important factor in determiningpower consumption, but P_(Static) is determined by a semiconductorfabrication process and an industry based technology, whereasP_(Dynamic) is changed depending on a system design. In view of a systemdesigner, reducing the dynamic power consumption is the target of apower save system design.

A VHT mode which is under discussion can use eight antennas or sixteenantennas and is very likely to support an 80-MHz bandwidth. For example,a multi-user multiple antenna technique can be applied in such a mannerthat an access point uses sixteen antennas and stations use fourantennas. It is expected that a multi-channel transmission technique canbe applied using a bandwidth of up to 160 MHz.

Therefore, a VHT standard station has two to eight times the antennasand bandwidth of the conventional standard station. The increase in thetransmission paths due to the increased antennas means the increase inthe size of the circuit and chip, which causes the increase in powerconsumption. In addition, the increase in the bandwidth used means theincrease in the required operating frequency, which also causes theincrease in the power consumption.

In the existing 802.11a/b/g/n wireless LAN standard, 802.11 Legacy PSM,802.11e Automatic Power Save Delivery (APSD), 802.11n Power Save MultiPoll (PSMP), Spatial Multiplexing (SM) Power Save modes have been usedas the power save technique. The conventional art has the following fiveproblems.

First, an awake mode station must be always in a reception-ready state.Second, a PSM, APSD or PSMP scheme requires a separate control signaland a large buffer size. Third, a MAC level power save techniquerequires a response delay time. Fourth, the IEEE 802.11n SM Power Savemode scheme is effective in the multi-antenna system, but the powerconsumption efficiency of single-path circuits is still low. Fifth, itis likely that the VHT mode will use an 80-MHz bandwidth. In this case,the sampling rate of the ADC and the DAC needs to be 160 MHz or more,which is four times higher than the existing IEEE. 802.11a/g. Sixth,since the power consumption is proportional to the operating frequencyand the circuit size, it is necessary to minimize the operatingfrequency, the number of toggling, and the number of operating circuits.Regarding this, the conventional art reaches a limit.

The conventional power save technique has been carried out in a MAClayer. However, as described above, in order to extend a battery chargecycle of a portable station by improving the power consumptionefficiency of a more complicated system, there is a need for a crosslayer power save technique which supplements the problems of the powersave technique of the MAC layer by using the physical layer technique.

Therefore, the power save technique which is the first part of thepresent invention will be described below. The cross layer power savemode (CL PS mode) will be referred to as a power save mode in theconstruction of the present invention which improves the powerconsumption efficiency by using both the power save mode techniques ofthe physical layer and the MAC layer.

1. Cross Layer Power Save Mode 1

In a reception-ready state of an awake period of a station, the stationimproves the dynamic power consumption efficiency by minimizing theoperating frequencies of the ADC or the DAC and the modem processor. Alegacy mode uses a bandwidth of 20 MHz, an HT mode can support abandwidth of up to 40 MHz, and a VHT mode can support a bandwidth of upto 80 MHz. Since a request-to-send frame and a clear-to-send frame aretransmitted in a legacy mode so that a legacy station can also receivethem, the ADC and the DAC use the operating frequency at a sampling rateof 40 MHz upon transmission/reception of RTS/CTS. When a data frame is aVHT mode, a sampling rate of 160 MHz is used in order to support abandwidth of up to 80 MHz. When a data frame is an HT mode, a samplingrate of 80 MHz is used to support a bandwidth of up to 40 MHz. When adata frame is a legacy mode, the operating frequency is transmitted at asampling rate of 40 MHz. The power consumption efficiency can beimproved by changing the sampling rate according to the data format.

In order to normally process a baseband signal in the digital modem eventhough the operating frequencies of the ADC and the DAC are changed, aprocedure of controlling an RF band stop filter bandwidth andcontrolling the operating frequencies of an interpolator and adecimator. The embodiment of the present invention includes a methodwhich controls a mode by a request frame and a response frame, forexample, RTS and CTS, or a control packet such as an ACK frame, and acontrolling apparatus therefore. That is, the use of the first crosslayer power save mode can improve the dynamic power consumptionefficiency by optimizing the operating frequencies of the ADC, the DAC,and the modem processor in the reception-ready state prior to thetransmission/reception of the request/response packet.

Such a method will be described below in detail.

In a legacy/HT/VHT hybrid mode BSS, a control signal such asrequest/response frames is transmitted and received in a legacy modeformat in order for compatibility. In this case, a station which is in areception-ready state in an awake mode improves the power consumptionefficiency by setting the sampling rate of the ADC to 40 MHz.

At this time, the RF center frequency and the analog band stop filtermay be reconfigured. In addition, the band stop filter of the digitalfilter may be reconfigured. Furthermore, the operating frequency of adecimator included in a receiving unit is reconfigured.

A transmitting unit transmits RTS/CTS in such a state that the samplingrate of the DAC is lowered to a 40-MHz bandwidth. In addition, in thetransmitting unit, the RF center frequency, the analog band stop filter,and the digital band stop filter may be reconfigured as in the receivingunit. In addition, the operating frequency of an interpolator includedin the transmitting unit may be reconfigured.

The station which transmits and receives the request/response frameschanges to a maximum supportable operating frequency in order totransmit and receive the data packet. The station which successfullyreceives ACK again changes to the power save mode when a transmissionopportunity period is ended. In addition, the station which transmitsACK and confirms no retransmission again changes to the power save mode.The above-described cross layer power save mode 1 can be used togetherwith the conventional art.

2. Cross Layer Power Save Mode 2

In the reception-ready state of the awake period, power is supplied toonly a carrier sensing related block prior to a carrier sensing, andpower of the other blocks is interrupted. In order for a power save modeoperation of a wireless communication system using a multi-antennatechnique, the conventional SM power save technique enables a fewreception paths and disables the others prior to the transmission andreception of RTS and CTS packets. In this method, a few reception pathsmust be enabled so that they are in a reception-ready state. On theother hand, when the cross layer power save mode 2 in accordance withthe embodiment of the present invention is used, the power is suppliedto only the carrier sensing related block provided at a front stage of amodem unit and is interrupted to the other blocks prior to the carriersensing, and the power is then supplied to the other blocks after thecarrier sensing. Hence, the power consumption efficiency can be furtherimproved. In addition, the conventional SM power save technique must useRTS and CTS. However, the cross layer power save mode 2 in accordancewith the embodiment of the present invention need not use RTS and CTS.

The cross layer power save mode 2 in accordance with the embodiment ofthe present invention will be described below in more detail.

The cross layer power save mode 2 is a use invention of Korean PatentApplication No. 10-2008-0127376 (U.S. patent application Ser. No.12/561076). The cross layer power save mode 2 of this patent applicationfocuses on a physical layer power save technique, but the presentinvention is improved to a cross layer power save mode technique andinterworks with the cross layer power save mode 1 to achieve theperformance improvement, which will be described later in a cross layerpower save mode 3.

Since the receiving end of the wireless communication system cannotpredict when a signal will be inputted, it is always in areception-ready state in an awake state. Thus, the dynamic powerconsumption efficiency of the receiving circuit is degraded. Theembodiment of the present invention uses the conventional method ofsupplying the power to only the carrier sensing related block prior tothe carrier sensing and supplying the power to the other blocks afterthe carrier sensing, and also uses a method of interrupting the power ofthe carrier sensing related block in a doze mode which is a MAC levelpower save mode. Hence, the power consumption efficiency can be furtherimproved.

FIGS. 1A and 1B are block diagrams of a wireless communication stationhaving three reception paths.

FIGS. 1A and 1B illustrate an example of a multi-antenna system.Reference numerals for the same parts processing signals received fromthe respective antennas are omitted. In addition, the parts to whichreference numerals are not assigned perform the same operations as theparts to which reference numerals are representatively assigned, aduplicate description thereof will be omitted. Furthermore, FIGS. 1A and1B are connected to form a single drawing. That is, the output signalsof FIG. 1A are inputted to FIG. 1B, and such an input/output relation isillustrated therein.

In an RF block 100 which processes RF signals received from theantennas, only a low noise amplifier (LNA) 101 and a voltage-controlledgain amplifier (VGA) 102 are illustrated. The LNA 101 amplifies thesignals received from the antennas while suppressing noise, and VGA 102performs an amplification operation thereon. The RF block 100 convertsan RF frequency band signal into a desired band signal, and converts ananalog signal into a digital signal through an ADC 111. The digitalsignal is inputted to a DC canceller 112, an energy detector 121, anautomatic gain controller (AGC) 131, and a saturation based carriersensor 132. The DC canceller 112 cancels a DC component from the digitalsignal. The signal from which the DC component is cancelled is inputtedto an FQ channel signal comparator 113. The output signal of the I/Qchannel signal comparator 113 is inputted to a buffer 115 and a channelmixer 141. The signal inputted to the buffer 115 is read in units of aspecific period and is inputted to a carrier frequency offset (CFO)estimator 116. The CFO corrector 116 detects and controls a carrierfrequency offset.

An output signal of the CFO corrector 116 is fast-Fourier-transform(FFT) processed by an FFT processor 117. That is, a time-domain signalis transformed into a frequency-domain signal. The frequency-domainsignal is phase-compared by a phase comparator 118 and is detected as asignal based on each antenna, each band, or each stream by a MIMOdetector 119. The signal detected by the MIMO detector 119 is inputtedto a demapper 120. The demapper 120 demaps the signal based on eachantenna, each band, or each stream.

The energy detector 121 receiving the digital signal outputted from theADC 111 detects energy of the digital signal, and outputs it to a clearchannel assessment (CCA) 122. The CCA 122 detects whether a signalexists on a channel and notifies the detection result to a MAC layer.The saturation based carrier sensor 132 receiving the digital signalfrom the ADC 111 determines saturation or non-saturation by detectingthe carrier signal, and provides signal level information to the AGC131. The AGC 131 uses the received digital signal to control gains ofthe LNA 101 and the VGA 102, based on the signal level informationreceived from the saturation based carrier sensor 132.

Meanwhile, the channel mixer 141 receiving the output signals of the I/Qchannel comparators 113 mixes the received signals. An LPF/averagingunit 142 low-pass-filters the received signal and calculates an averageby dividing a decimal value by 2. An output signal of the LPF/averagingunit 142 is inputted to a receive signal strength indicator (RSSI)sensor 123, an RSSI based carrier sensor 143, an auto correlator 144,and a cross correlator 145. The RSSI sensor 123 measures an RSSI of areceived signal and provides the measured RSSI to the CCA 122. When acarrier signal is detected, the RSSI based carrier sensor 143 measuresan RSSI of the detected carrier signal. The auto correlator 144 and thecross correlator 145 calculate correlation values. A CFO estimator 146estimates a CFO and provides the estimation result to a framesynchronizer 147. The frame synchronizer 147 receives signals from theRSSI based carrier sensor 143, the cross correlator 145, the saturationbased carrier sensor 132, and the CFO estimator 146, and detects a framesynchronization. In addition, the CFO estimator 146 provides theestimated value to a CRO corrector 117 provided at each antenna. An XCRbased carrier sensor 148 calculates an XCR.

In addition, the FFT processor 117 provides the FFT-processedinformation to a CFO/phase estimator 151 and estimates a CFO and aphase. The estimated phase information is provided to the phasecomparator 118. In addition, the FFT processor 117 receives informationfrom the channel estimator 152 and performs channel estimation. Usingthe channel estimation information performed at the channel estimator152, the MIMO detector 119 outputs the signal based on each stream.

Soft demappers perform a demapping based on each stream, and adeinterleaver deinterleaves the output of the corresponding demapper. Adeparser inserts necessary information into the deinterleavedinformation, and a decoder decodes the resulting signal. Then, adescrambler descrambles the signal and transfers the descrambled signalto the MAC layer.

In the above-described architecture of FIGS. 1A and 1B, a power sourceand a power source controller are not illustrated. The operations of thepower source and the power source controller will be described later. Inaddition, a block 150 indicated by dotted lines of FIG. 1A is related toa carrier sensing. Power is supplied to only the block 150 in an awakemode. When the carrier is sensed, power is supplied to the other blocks.Furthermore, in FIGS. 1A and 1B, the parts other than the MAC layercorrespond to a physical layer part.

A difference from the conventional art is as follows.

1) A 4-stage cross layer power save mode wireless communication systemhas four states: a doze state, a state prior to RTS/CTS reception of anawake mode, a state after an RTS/CTS reception of an awake mode beforedata reception, and a data receiving state. In accordance with theembodiment of the present invention, the power save mode is optimizedaccording to the four reception states. That is, in the doze mode, allblocks except for a MAC timer are turned off. In the awake mode, onlythe carrier sensing blocks of a few paths (one or more than two) areturned on. After the RTS/CTS reception, the other blocks of a few pathsare turned on. Upon the data reception, all blocks of all paths areturned on.

2) The embodiment of the present invention relates to a cross layerpower save technique using both a power save technique of a physicallayer and a power save technique of a MAC layer, which can improve thepower consumption efficiency, as compared to the conventionalsingle-layer power save technique.

FIG. 2 is a flowchart in a power save mode change in accordance with anembodiment of the present invention.

At step 200, a wireless LAN device determines whether or not it is in anawake state. If so, the wireless LAN device proceeds to step 206;otherwise, the wireless LAN device proceeds to step 202. At step 202,the wireless LAN device determines whether or not a timer is terminated.If so, the wireless LAN device proceeds to step 206; otherwise, thewireless LAN device proceeds to step 204 to turn off power of all blocksand returns to step 200.

When the wireless LAN device is at step 200 or when the wireless LANdevice proceeds from step 202 to step 206, power is supplied to only oneor two reception part carrier sensing blocks. When the wireless LANdevice is awake due to the termination of the timer or it is in theawake mode, it is prior to the carrier sensing. Thus, it is in theabove-described second reception state, that is, the state prior to theRTS/CTS reception.

After the power is supplied to only the carrier sensing blocks, thewireless LAN device proceeds to step 208 to determine whether thecarrier sensing is performed within a predetermined time. When thecarrier sensing is performed, the wireless LAN device proceeds to step210; otherwise, the wireless LAN device proceeds to step 206.

When the carrier sensing is performed, the wireless LAN device proceedsto step 210 to supply power to the remaining blocks of the receptionpath. Then, the wireless LAN device proceeds to step 212 to determinewhether or not a packet category can be used. That is, the wireless LANdevice determines whether or not the packet kind information can beused. When it is determined that the packet category, such as RTS/CTS,can be used, the wireless LAN device proceeds to step 214; otherwise,the wireless LAN device proceeds to step 216.

At step 214, the wireless LAN device determines or not whether thereceived packet category is the RTS/CTS packet. When it is determinedthat the received packet category is the RTS/CTS packet, the wirelessLAN device proceeds to step 218 to supply the power to the correspondingblocks of the reception path according to the number of streams.

On the other hand, when it is determined at step 214 that the receivedpacket category is not the RTS/CTS packet, or it is determined at step212 that the packet category cannot be used, the wireless LAN deviceproceeds to step 216 to supply the power to the blocks of all receptionpaths.

In summary, in the doze mode, the power supplied to all blocks isinterrupted until the timer is terminated. When the timer is terminated,the power is supplied to only the path necessary for the carrier sensingand the corresponding carrier sensing blocks. When the carrier sensingis performed in the awake mode, the power is supplied to the otherblocks of the corresponding path for the carrier sensing. When thepacket kind information can be used and the received packet is theRTS/CTS, more paths can be turned on in order to improve the carriersensing result of the data packet. When the packet kind informationcannot be used or the received packet is the data packet, all paths areturned on.

FIG. 3 is a timing diagram for helping the understanding of theoperation principle of the four reception modes in accordance with anembodiment of the present invention.

In the doze mode 300, all blocks of the receiver are in the turned-offstate 310. The awake mode 310 is divided into three cases. The firststate 311 is a state in which the power is supplied to only the carriersensing blocks corresponding to one or two reception paths for thecarrier sensing. In the state 312, the received packet category or thepacket reception is detected and the power is supplied to the blockscorresponding to one or two reception paths. That is, when the RTS (321)frame is received, the power is supplied to only the blocks forreceiving the RTS frame. In the state 313, when the data frame 323 isreceived, the power is again supplied to all blocks corresponding to thereception path. After all data frames are received, the state changes tothe state 314 in which the power is supplied to only the blocks forcarrier sensing. In this state, the frames such as the ACK frame 324 canbe received. When the ACK frame is received and then no signal isdetected for a predetermined time, that is, until the preset timer isterminated, the wireless LAN device again enters the doze mode 300 toturn off all blocks.

That is, as described above with reference to FIG. 3, the correspondingstation can operate in the doze mode or the awake mode in such asituation that RTS, CTS, data, and ACK frame are sequentiallytransmitted and received. In the awake mode, it can be determinedwhether or not to supply the power and clock to the internal receptionblocks according to the carrier sensing and the kind of the frame in theawake mode.

FIG. 4 is a finite state machine of a cross layer power save mode 2.

In FIG. 4, an idle state 410 refers to one or all states among aninitial state and/or a standby state and/or a power off state. When thepower is on in the idle state 410, a start state 411 begins. When acarrier is sensed in a carrier sensing (CS) state 412, it enters anenable additional radios state 413. Then, it changes to an AGC state 414which controls a gain of a received signal by a counter value. In theAGC state 414, the gain of the received signal is controlled. When thegain of the received signal is controlled, it changes to a CFOestimation state 415 by using a short preamble. When the CFO estimationis roughly completed, it changes to a synchronization state 416 forsynchronization of the signal provided from the system, that is, theframe. When the synchronization is acquired, it changes to a CFOestimation state 417 by using a long preamble. That is, the CFO iscompensated and the temporary synchronization is acquired in the CFOestimation state 415 and the synchronization state 416.

When the CFO estimation is well completed using the long preamble, itchanges to a signal field decoding state 418. In the signal fielddecoding state 418, the signal decoding is performed. When the signaldecoding is validly completed, it changes to a data decoding state 419.When the data decoding is completed, it changes to an end state 420 andagain changes to the idle state 410.

When the carrier is not detected in the CS sensing state 412, thecarrier sensing state is continuously maintained. When the automaticgain control is failed in the AGC state 414, it changes to the idlestate 210. As other cases of changing to the idle state, the followingcases exist. The first case is a case in which the rough CFO estimationis impossible in the CFO estimation state 417 using the long preamble.The second case is a case in which the synchronization is impossible inthe synchronization state 416. The third case is a case in which theexact CFO estimation is impossible in the CFO estimation state 417 usingthe long preamble. The fourth case is a case in which the signal fielddecoding is failed in the signal field decoding state 418.

In the finite state machine of FIG. 2, while it maintains the CS state,the power consumption is minimized by using a method of interrupting thesupply of power and clock to the sub blocks corresponding to allsubsequent states. By using such a state change, both the carriersensing method and non-carrier sensing method can be applied.

Meanwhile, the idle state 410 is continuously maintained even in thedoze mode or the sleep mode. In the doze mode, the carrier sensingblocks are turned off and are in the idle state. Then, when the timer ofthe MAC layer is terminated and it changes to the awake mode, it goesthrough the start state 411 and waits until the carrier is sensed in thecarrier sensing state 412. At this time, only the carrier sensing blockamong the receiving ends of the station is turned on. Thus, the powerconsumption efficiency can be improved. After the carrier sensing, allblocks of the corresponding paths are turned on to process the signals.

FIG. 5 is a timing diagram for helping the understanding of a powercontrol step in accordance with an embodiment of the present invention.

As illustrated in FIG. 5, the receiver in accordance with the embodimentof the present invention coexists in the awaken mode 500 and the dozemode 510. In the awaken mode 500, it is divided into a carrier sensingperiod CP and a carrier non-sensing period Non-CP in a physical layerpower saving timing (PHY PS timing) The carrier sensing period CP isended at the time point 501 when the carrier is sensed, and the packet 1521 after the carrier sensing is being sensed during the carriernon-sensing period Non-CP. In the doze mode, the power of all blocks isinterrupted. This is called the doze period DP.

As such, in the physical layer, no clock is provided to the physicallayer blocks, to which the power is not supplied, in order to reduce thepower consumption in the carrier sensing period CP. This can beconfirmed by the physical layer power saving clock (PHY PS clock) andthe physical layer carrier sensing valid information (PHY CS valid)illustrated in FIG. 5.

Meanwhile, in the MAC layer, the power saving clock (MAC PS clock) issupplied only from the carrier sensing period (CP) necessary for thecarrier sensing. To detecting the carrier sensing, it can be confirmedfrom the MAC carrier sensing valid (MAC CS valid) information. Theseperiods are maintained up to the time point when the doze mode begins.

As described above, the power save modes of the MAC layer and thephysical layer are interworked to ensure the efficient power consumptionefficiency, as compared to the case in which the MAC layer or thephysical mode alone is used.

3. Cross Layer Power Save Mode 3

The cross layer power save mode 3 in accordance with the embodiment ofthe present invention is a hybrid mode of the cross layer power savemode 1 and the cross layer power save mode 2. In the cross layer mode 1,the cross layer mode 1 is controlled by the carrier sensing result ofthe cross layer mode 2, without any aid of the request/response frameand the ACK frame. Hence, as compared to the cross layer mode 1, thepower consumption efficiency can be improved by reducing the dynamicpower consumption for an interframe space (IFS) time (16 us) and thecarrier sensing time (about 2 us) due to the cross layer mode 2. Thecross layer power save mode 3 can change a power save mode by thecarrier sensing result, without RTS/CTS, unlike in a case in which theRTS/CTS is used in the cross layer power save mode 1.

According to the cross layer power save mode 1 described above, the RFunit converts the signal passing through the 20-MHz band stop filterinto a digital signal at a sampling rate of 40 MHz and the carrier issensed.

In addition, after the carrier is sensed by the cross layer power savemode 2, the blocks other than the carrier sensing are operated.

When the packet is received in such a manner, the receiver of thewireless LAN system is operated using the maximum sampling rate.

At this time, when the kind of the data packet to be received can bepreviously known by the request/response packet, the sampling rate canbe determined according to the mode of the received packet, not themaximum sampling rate.

In addition, during the above procedure, a process of changing theoperating frequency of the interpolator and the decimator andreconfiguring the RF analog band stop filter and the digital band stopfilter is included.

In the method in accordance with the third embodiment of the presentinvention, the sampling rate of the modem unit for processing a basebandsignal can be optimized to the corresponding mode.

The configuration and operation of the cross layer power save mode hasbeen described above. A transmitting method for improving the efficiencyof the cross layer power save mode described above will be described asthe second part of the present invention.

The information of the frame to be received by the receiving end isincluded in the request frame or the response frame and then istransmitted. Thus, the receiving end can be waited in a state optimizedto the corresponding bandwidth. That is, next transmission modeinformation of the data frame to be transmitted after therequest/response frame, for example, RTS/CTS frames, is informedtogether. Thus, the reception mode, such as the analog/digital filtersetting, the RF center frequency setting, or the operating frequencysampling rate, is optimized to the kind of the frame to be received,thereby improving the throughput and improving the power consumptionefficiency.

1) In this case, the required performance index value and transmissionstream number are as follows.

-   -   When the stream number of the transmit signal is smaller than        the number of the receive antennas, all multi-antennas are not        necessarily used and the number of antennas to be used can be        selected according to the required performance index value. The        required performance index may include a contents category or a        link performance value, for example, a signal to noise ratio or        a channel variation.

2) The transmission packet mode, the channel bandwidth to be used, andthe transmission transmitting method are as follows.

-   -   After receiving the request/response packet, the optimized        operating frequency for the corresponding packet mode can be        used, without changing to the maximum operating frequency which        can be supported by the receiver.    -   In addition, since the optimal filter for the received signal        can be applied, the detection reliability of the receiving end        can be improved.    -   In addition, a green field mode operation can be performed        during the transmission opportunity period.

Consequently, the throughput and the power consumption efficiency can beimproved.

A method for previously notifying information for transmission will bedescribed below. It is assumed that a first node and a second nodecommunicate with each other. The first node or the second node candetermine whether a correspondent node includes the channel stateinformation or the data frame mode information, based on the dynamicchannel bandwidth allocation supportable bit of the request frame or theresponse frame, for example, 1 bit value.

The transmission mode information of the request/response frame may beincluded in the request/response frame and transmitted as in thefollowing embodiment. However, it should be noted that the invention isnot limited to the following embodiment, and the invention can berealized while maintaining the conventional standard and compatibilityby using a reservation bit remaining the request/response frame.

-   -   1) A service field of a physical layer    -   2) A duration field of a MAC header    -   3) a frame control field of the MAC header

For example, four bandwidth support modes can be set using two bits inthe service field or the duration field. The four bandwidth supportmodes may be divided as follows.

-   -   00: 20 MHz,    -   01: 40 MHz,    -   10: 80 MHz,    -   11: 160 MHz

The information of the next frame which is included in therequest/response frame may be used in order for noise reduction andmulti-mode frame coexistence (20/40/80/160 MHz bandwidth or thelegacy/HT/VHT mode), not for the power save mode.

FIGS. 7 and 8 are timing diagrams for noise reduction and a multi-modeframe coexistence in accordance with an embodiment of the presentinvention.

First, referring to FIG. 7, a frame 711 in which four 20-MHz bandwidthRTSs are bonded is transmitted to an entire 80-MHz band before dataframe transmission in order to transmit a 20-MHz bandwidth data frame tothe node 1 and the node 2. In this way, the node 1 is in a standby stateby setting network allocation vector (NAV) values of various nodessupporting adjacent 20/40/80 MHz bandwidths, not its own frame. On theother hand, the node 2 recognized as its own frame changes the centerfrequency and a filter of a receiving end, based on the bandwidth valueset in the frame 711 in which the four RTSs are bonded, and transmits aCTS frame 712 over a 20-MHz band. The node 1 receiving the CTS frame 712transmits a 20-MHz bandwidth data frame 713. The node 2 reconfigured tobe suitable for the reception of the data frame 713 receives the dataframe 713 and then transmits an ACK frame 714 when the received dataframe is correctly recovered.

FIG. 8 illustrates the above-described embodiment of FIG. 7 which isdivided based on a channel bandwidth. That is, RTS frames 811, 812, 813and 814 are transmitted over the 80-MHz bandwidth. By using thebandwidth information values set to the RTS frames 811, 812, 813 and814), noise and power consumption can be reduced when transmitting orreceiving the CTS frame 821, the data frame 831, and the ACK frame 841 mwhich are the 20-MHz bandwidth mode.

FIG. 9 is a diagram for explaining the operation of the presentinvention in an overlapped basic service set (OBSS) situation. In aBSS1, when an AP1 transmits the RTS frame in order to transmit data to astation STA, four 20-MHz band RTSs are simultaneously transmitted on theassumption that it is known that a station supporting a band of up to 80MHz is included. At this time, when a BSS2 transmits a 40-MHz bandsignal, the AP1 does not know whether an interference signal exists.

At this time, the station transmits the CTS through the 40-MHz bandexcept for the band influenced by the interference signal, and the AP1transmits the data frame through the 40-MHz band through which the CTSis received. At this time, the station must be able to discriminate theinterference signal and a signal to be received. Since APs have theirinherent BSS identification (BSSID), it can be determined whether thereceived packet is a packet outputted from the BSS where the station isincluded, or a packet outputted from an external BSS, based on the BSSIDincluded in the MAC header. The interference signal is discriminated andCTS is transmitted over a band in which an interference signal area isexcluded from a band confirmed by RTS. The AP1 can transmit data over aband at which CTS is received. In addition, the occupied bandwidth canbe minimized through the above procedure. The frequency resources can beefficiently used and the power consumption efficiency can be improved.

Finally, the embodiment of the present invention includes a power savemode of a multi-channel transmitting method which is to be used as anext generation wireless LAN technique. The next generation wireless LANtechnique transmits data using an 80-MHz bandwidth, which is four timesor two times wider than the existing 20-MHz or 40-MHz bandwidth. Thus,the throughput can be increased two times to four times. However, as thesampling rates of the ADC and the DAC are increased, the powerconsumption is also increased. In addition, since the modem processoruses a high operating frequency, the dynamic power consumptionefficiency is degraded. However, the station need not always use a highsampling frequency, and the power consumption efficiency can be improvedusing an appropriate sampling rate according to the mode and the kind ofthe packet used.

The power save mode for the conventional spatial multiplexing schemeimproves the power consumption efficiency by turning on a few receptionpaths and turning off the others prior to the reception of RTS/CTS.However, the power save mode for the multi-channel scheme in accordancewith the embodiment of the present invention uses a sampling rate atwhich a legacy mode packet can be received prior to the reception ofRTS/CTS, and controls the sampling rate according to the correspondingmode packet or the used mode after the reception of RTS/CTS. Acontrolling apparatus can change to a corresponding mode when a kind ofa next data packet or mode information to be used can be transmittedover the RTS/CTS packet, and, if not, controls to a maximum samplingrate for a mode which is supported by the corresponding station.

The embodiment of the present invention can support both the continuousmulti-channel transmission scheme and the discontinuous multi-channeltransmission scheme. That is, when the multi-channel is continuous, itoperates with the increase/decrease of a sampling rate. However, whenthe multi-channel is discontinuous, the power consumption efficiency canbe improved by determining whether to use a discontinuous path.

FIG. 6 is a flowchart of a change procedure in a multi-channel powersave mode in accordance with an embodiment of the present invention.

At step 600, a wireless LAN receiver determines whether or not it is inan awake state. If so, the wireless LAN receiver proceeds to step 606;otherwise, the wireless LAN receiver proceeds to step 602. At step 602,the wireless LAN receiver determines whether or not a timer isterminated. If so, the wireless LAN receiver proceeds to step 606;otherwise, the wireless LAN receiver proceeds to step 604 to turn offpower of all blocks and returns to step 600.

When the wireless LAN receiver is at step 600 or when the wireless LANreceiver proceeds from step 602 to step 606, power is supplied to onlyone or two reception part carrier sensing blocks. At this time, thewireless LAN receiver operates at a sampling rate of a legacy mode. Whenthe wireless LAN receiver is awake due to the termination of the timeror it is in the awake mode, it is prior to the carrier sensing. Thus, itis in the above-described second reception state, that is, the stateprior to the RTS/CTS reception.

After the power is supplied to only the carrier sensing blocks, thewireless LAN receiver proceeds to step 608 to determine whether thecarrier sensing is performed within a predetermined time. When thecarrier sensing is performed, the wireless LAN receiver proceeds to step610; otherwise, the wireless LAN receiver proceeds to step 606.

When the carrier sensing is performed, the wireless LAN receiverproceeds to step 610 to supply power to the remaining blocks of thereception path. At this time, the sampling rate may use a sampling rateof the legacy mode. In this way, the sampling rate is reduced andtherefore the power consumption is reduced. Then, the wireless LANreceiver proceeds to step 612 to determine whether or not a packetcategory can be used. That is, the wireless LAN receiver determineswhether or not the packet kind information can be used. When it isdetermined that the packet category, such as RTS/CTS, can be used, thewireless LAN receiver proceeds to step 614; otherwise, the wireless LANreceiver proceeds to step 616.

At step 614, the wireless LAN receiver determines or not whether thereceived packet category is the RTS/CTS packet. When it is determinedthat the received packet category is the RTS/CTS packet, the wirelessLAN receiver proceeds to step 618 to supply the power to thecorresponding blocks of the reception path according to the number ofstreams.

On the other hand, when it is determined at step 614 that the receivedpacket category is not the RTS/CTS packet, or it is determined at step612 that the packet category cannot be used, the wireless LAN receiverproceeds to step 616 to supply the power to the blocks of all receptionpaths.

Then, the wireless LAN receiver proceeds to step 620 to determinewhether or not mode information can be used. The mode information istransmitted in the above-described manner. When the mode informationcannot be used, the wireless LAN receiver proceeds to step 622 tooperate at a maximum data rate which can be supported by the receiver.

On the other hand, when the mode information can be used, the wirelessLAN receiver proceeds to step 624 to determine whether or not thecurrent mode is the legacy mode. When it is determined at step 624 thatthe current mode is the legacy mode, the wireless LAN receiver proceedsto step 626 to operate at a sampling rate of the legacy mode. When it isdetermined at step 624 that the current mode is not the legacy mode, thewireless LAN receiver proceeds to step 628 to determine whether or notthe current mode is the HT mode. When it is determined that the currentmode is the HT mode, the wireless LAN receiver proceeds to step 630 tooperate at a sampling rate corresponding to the HT mode.

However, when it is determined at steps 624 and 628 that the currentmode is neither the legacy mode nor the HT mode, the current mode is theVHT mode. Therefore, the wireless LAN receiver proceeds to step 632 todetermine whether or not the data stream is contiguously received. Whenit is determined that the data stream is contiguously received, thewireless LAN receiver proceeds to step 634 to operate at the samplingrate of the VHT mode. However, when it is determined that the datastream is not contiguously received, the wireless LAN receiver proceedsto step 636 to perform a multi-channel power saving operation.

FIG. 6 illustrates the change order of the power save mode according tothe above-described four reception states. That is, in the doze mode,all blocks are turned off until the timer is terminated. When the timeris terminated, the power is supplied to only the path necessary for thecarrier sensing and the corresponding carrier sensing blocks. At thistime, since the RTS/CTS is transmitted in the legacy mode, the operatingfrequency for the legacy mode is set. When the carrier sensing isperformed in the awake mode, the power is supplied to the other blocksof the corresponding path for the carrier sensing. When the packet kindinformation can be used and the received packet is the RTS/CTS, morepaths can be turned on in order to improve the carrier sensing result ofthe data packet. When the packet kind information cannot be used or thereceived packet is the data packet, all paths are turned on. At thistime, the corresponding station changes to a maximum supportableoperating frequency so that it can process any kind of a packet. In acase in which the packet kind information can be used and thus thepacket is the RTS/CTS packet, it changes to a sampling rate suitable forthe corresponding mode when the mode information can be used. When themode information cannot be used, the corresponding station changes tothe maximum supportable sampling rate so that it can process a packet ofany mode. When the mode is the packet of the VHT mode, the power andclock may not be supplied to the paths for the discontinuous channelwhich is used as the above-described power save mode for themulti-channel transmission.

INDUSTRIAL APPLICABILITY

The present invention can be used in a wireless LAN system and the like.

1. A method of accessing a channel in a wireless local area network,performed by a transmitter comprising a Medium Access Control (MAC)layer and a physical (PHY) layer, the method comprising: generating arequest to send (RTS) frame at the MAC layer; generating a PHY frame atthe PHY layer, the PHY frame including a service field and the RTSframe; transmitting the PHY frame to a station over a first bandwidth;and receiving a clear to send (CTS) frame over a second bandwidth fromthe station in response to the RTS frame, wherein the service fieldindicates the first bandwidth, and wherein the second bandwidth is equalor less than the first bandwidth.
 2. The method of claim 1, wherein thefirst bandwidth is one of 20 MHz, 40 MHz, 80 MHz and 160 MHz, and thesecond bandwidth is one of 20 MHz, 40 MHz, 80 MHz and 160 MHz.
 3. Themethod of claim 1, wherein the PHY frame is duplicately transmitted overeach 20 MHz of the first bandwidth.
 4. The method of claim 1, whereinthe CTS frame is duplicately received over each 20 MHz of the secondbandwidth.
 5. An apparatus of accessing a channel in a wireless localarea network, the apparatus comprising: a transmitter comprising aMedium Access Control (MAC) layer and a physical (PHY) layer andconfigured to: generate a request to send (RTS) frame at the MAC layer;generate a PHY frame at the PHY layer, the PHY frame including a servicefield and the RTS frame; transmit the PHY frame to a station over afirst bandwidth; and a receiver configured to receive a clear to send(CTS) frame over a second bandwidth from the station in response to theRTS frame, wherein the service field indicates the first bandwidth, andwherein the second bandwidth is equal or less than the first bandwidth.6. The apparatus of claim 5, wherein the first bandwidth is one of 20MHz, 40 MHz, 80 MHz and 160 MHz, and the second bandwidth is one of 20MHz, 40 MHz, 80 MHz and 160 MHz.
 7. The apparatus of claim 5, whereinthe PHY frame is duplicately transmitted over each 20 MHz of the firstbandwidth.
 8. The apparatus of claim 5, wherein the CTS frame isduplicately received over each 20 MHz of the second bandwidth.
 9. Anapparatus of accessing a channel in a wireless local area network, theapparatus comprising: a receiver configured to receiving a request tosend (RTS) frame over a first bandwidth from a station; and atransmitter comprising a Medium Access Control (MAC) layer and aphysical (PHY) layer and configured to: generate a clear to send (CTS)frame at the MAC layer; generate a PHY frame at the PHY layer, the PHYframe including a service field and the CTS frame; transmit the PHYframe to the station over a second bandwidth in response to the RTSframe; and wherein the service field indicates the second bandwidth, andwherein the second bandwidth is equal or less than the first bandwidth.10. The apparatus of claim 9, wherein the first bandwidth is one of 20MHz, 40 MHz, 80 MHz and 160 MHz, and the second bandwidth is one of 20MHz, 40 MHz, 80 MHz and 160 MHz.
 11. The apparatus of claim 9, whereinthe PHY frame is duplicately transmitted over each 20 MHz of the secondbandwidth.
 12. The apparatus of claim 9, wherein the RTS frame isduplicately received over each 20 MHz of the first bandwidth.